Classic BPF filters using a variable offset into the packet, such as
"tcp[tcpflags] & tcp-syn != 0" or "tcp[0:4] = ...", read the wrong bytes.
The indirect loads ldb/ld [x + k] were handled in the same case as the
arithmetic instructions, which take the source register from
BPF_SRC(code), that is bit 0x08. In a load opcode that bit is part of
the size field, not a K/X selector, so BPF_LD|BPF_IND|BPF_B (0x50) and
BPF_LD|BPF_IND|BPF_W (0x40) both yield BPF_K and the index register
becomes R0 (A) instead of R7 (X). The halfword form works only because
BPF_H and BPF_X are both 0x08.
Give the indirect loads their own case next to the absolute loads and
emit X as the index register. The interpreter and the JITs already
take the index from src_reg, so this fixes all engines.
Bugzilla ID: 2085
Fixes: 2eccf6afbea9 ("bpf: add function to convert classic BPF to DPDK BPF")
Cc: [email protected]
Signed-off-by: Stephen Hemminger <[email protected]>
---
lib/bpf/bpf_convert.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/lib/bpf/bpf_convert.c b/lib/bpf/bpf_convert.c
index 37095eea52..a32e1cdd8a 100644
--- a/lib/bpf/bpf_convert.c
+++ b/lib/bpf/bpf_convert.c
@@ -301,6 +301,13 @@ static int bpf_convert_filter(const struct bpf_insn *prog,
size_t len,
*insn = BPF_RAW_INSN(fp->code, 0, 0, 0, fp->k);
break;
+ /* Indirect loads index the packet with X: A = P[X + k]
*/
+ case BPF_LD | BPF_IND | BPF_W:
+ case BPF_LD | BPF_IND | BPF_H:
+ case BPF_LD | BPF_IND | BPF_B:
+ *insn = BPF_RAW_INSN(fp->code, 0, BPF_REG_X, 0, fp->k);
+ break;
+
case BPF_ALU | BPF_DIV | BPF_X:
case BPF_ALU | BPF_MOD | BPF_X:
/* For cBPF, don't cause floating point exception */
@@ -328,9 +335,6 @@ static int bpf_convert_filter(const struct bpf_insn *prog,
size_t len,
case BPF_ALU | BPF_DIV | BPF_K:
case BPF_ALU | BPF_MOD | BPF_K:
case BPF_ALU | BPF_NEG:
- case BPF_LD | BPF_IND | BPF_W:
- case BPF_LD | BPF_IND | BPF_H:
- case BPF_LD | BPF_IND | BPF_B:
/* All arithmetic insns map as-is. */
insn->code = fp->code;
insn->dst_reg = BPF_REG_A;
--
2.53.0
